<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    canvas{
    background-color: rgba(255,0,0,0.1);
    }
    body{
        margin: 0;
        
    }
</style>
<body>
 <canvas id="tutorial" width="300" height="300px">
    如果您的浏览器不兼容,请升级.
 </canvas>     

</body>
<script>
    window.onload = function()
    {
     let canvasEl=document.getElementById("tutorial");

     if(!canvasEl.getContext){
        return;
     }
    let ctx = canvasEl.getContext('2d');
 console.log(ctx);


ctx.fillRect(0,0,100,50)
     


    }
</script>
</html>